Grimes and Elon Musk have listed their son's name as X Æ A-XII Musk on his birth certificate.

Grimes and Elon Musk

Grimes and Elon Musk

The 32-year-old singer and the Tesla CEO welcomed their baby boy into the world on May 4, and it was later claimed the pair had chosen the unusual moniker - at the time stylised as X Æ A-12 - with the couple seemingly confirming the news in several social media posts.

And in a copy of the tot's birth certificate obtained by TMZ, it has now been officially confirmed they have indeed legally bestowed the name, written as X Æ A-XII, on their newborn son.

The document lists X as the first name of their son, whilst Æ A-XII is his middle name, and Musk is his surname.

The change to the spelling of X Æ A-XII's name comes after Grimes recently confirmed they had to make the alteration in order to comply with California law, which doesn't permit numbers to be used in names.

Grimes spoke about the change after an Instagram follower asked: "Did you change the baby name because of Californian laws ? What is the baby's new name? (sic)"

And she replied: "X Æ A-Xii (sic)"

The music star subsequently added: "Roman numerals. Looks better tbh (sic)"

The unusual moniker has also sparked debate over pronunciation, and Elon previously broke down each element of his son's name.

He said: "It's just the letter X and then the Æ is pronounced 'Ash. A-12 is my contribution.... Coolest plane ever. It's pretty great."

He also explained that Grimes "mostly came up with the name," adding: "Yeah, she's great at names."

And the SpaceX founder even corrected Grimes' explanation of their son's name after she took to Twitter to explain its origins.

She wrote: "X, the unknown variable ... Æ, my elven spelling of Ai (love &/or Artificial intelligence) ... A-12 = precursor to SR-17 (our favourite aircraft). No weapons, no defences, just speed. Great in battle, but non-violent + (A=Archangel, my favourite song) (metal rat) (sic)."

However, Musk couldn't help jumping into the comments to correct his partner.

He wrote: "SR-71, but yes," in reference to the aircraft and it didn't take Grimes, 32, long to put him in his place.

She tweeted: "I am recovering from surgery and barely alive so may my typos b forgiven but, damnit. That was meant to be profound (sic)."

Elon quickly backed down and wrote: "You are a powerful [fairy emoji, queen emoji]."